Grinding mill

ABSTRACT

A grinding mill comprises a grinding chamber at the bottom of which a rotatable plate is supported. The plate carries pivotable rollers which are urged against a rolling track fixed in the chamber at a higher level than the plate. An air distributor encircles the chamber at the level of the plate and has air inlets for producing an airflow in the chamber which conveys the ground material upwardly in an axial central region of the chamber for external discharge at the top thereof. The plate is driven in rotation from below so that the entire region of the chamber above the center of the plate is completely open.

United States Patent Inventor Jean Desbordes Paris, France Appl. No. 770,025 Filed Oct. 23, 1968 Patented June 29, 1971 Assignee Stein & Roubaix Paris, France Priority Oct. 25, 1967 France 125838 GRINDING MILL 5 Claims, 2 Drawing Figs.

US. Cl 241/52, 241/110, 241/130 Int. Cl B02c 15/08 Field of Search v. 241/110,

Primary ExaminerDonald G. Kelly AttorneyWaters, Roditi, Schwartz and Nissen ABSTRACT: A grinding mill comprises a grinding chamber at the bottom of which a rotatable plate is supported. The plate carries pivotable rollers which are urged against a rolling track fixed in the chamber at a higher level than the plate. An air distributor encircles the chamber at the level of the plate and has air inlets for producing an airflow in the chamber which conveys the ground material upwardly in an axial central re gion of the chamber for external discharge at the top thereof. The plate is driven in rotation from below so that the entire region of the chamber above the center of the plate is completely open.

E /2 /3 A? 11 7 E l GRINDKNG MILL The present invention relates to grinding mills having rollers which are pivotable in such manner that they can be applied against a rolling track by centrifugal force.

The grinding mills ofthis type heretofore proposed are pendular-body mills in which the rollers are suspended from a plate driven by a vertical shaft disposed on the axis of the mill. The product to be ground is introduced through a lateral chute, while an air vortex transverse the mill from bottom to top between the rollers and the rolling track, stirring in this way the product in the process of being ground and entraining the ground grains into a selector or separator at the top which allows only those particles which have attained the required fineness to pass; the other particles drop back by gravity to the bottom of the grinding mill, where they are picked up by blades driven rotatively at the same time as the pendular plate, to be subjected anew to the action of the rollers.

These pendular-body grinding mills of known type have a certain number of drawbacks. Thus, in order to drive the pendular plate, it is necessary to resort to a shaft of great height journaled in an upper bearing located in an extremely dusty and turbulent atmosphere and this poses problems of lubrication and tightness which are difficult to solve in a wholly satisfactory manner.

Moreover, as the shaft and the pendular plate occupy a considerable space in the center of the grinding mill, they prevent axial feed of the product, which may, however, prove to be useful, in particular for facilitating uniform distribution. Furthermore, the assembly consisting of the shaft and the pendular plate interferes with the flow of the air at the outlet of the mill, causing a considerable loss of pressure and promoting congestion of the mill.

Finally, the upper bearing located at a great distance from the lower bearing undergoes intense dynamic stresses which may result from a balancing defect of the movable assembly and/or from an ovalization of the rolling track as the result of irregular wear and and of the differential action of the rollers due to the heterogeneousness of the materials to be ground or to the irregularity of their distribution.

An object of the present invention is to remedy these drawbacks.

To this end, a grinding mill according to the invention is characterized by the fact that the rollers are supported from a plate disposed at the bottom of said grinding mill.

In a first constructional form, the rollers, which can turn on their own axis, are carried directly by the plate, being articulated thereto in such manner that they can be applied by the centrifugal force against a rolling track at a level above the plate.

According to another constructional form, each roller is supported from the plate through the medium of a stirrup from which it is suspended, the stirrup being articulated to the plate in such manner that it can be applied by the centrifugal force against a rolling track likewise located at a level higher than that of the plate.

With the arrangement according to the invention, the length of the shaft serving to drive the plate rotatively is considerably reduced and this results in better behavior under dynamic stresses and does away with the difficulties of lubrication and tightness. Moreover the center of the chamber is not obstructed as in the known constructions, so that it is possible to effect axial feed with crude product or to house the separator in the center, i.e., a dynamic separator functioning by a combination of a relaxation of pressure and the centrifugal action, in the grinding chamber itself. In the latter case, the total weight of the installation is considerably reduced and the reduction in height, which lowers the center of gravity, eliminates vibration.

According to another embodiment of the invention, there are provided at least two rolling tracks separated by deflectors and with which there cooperates rollers mounted according to the invention from one and the same bottom plate or from a plurality of different plates. With an apparatus constructed in this manner, it is possible to effect, in a single operation, crushing to very high degrees of fineness, while reducing the recycling circuits of the product and increasing the output of the apparatus.

Other features and advantages of the invention will appear in the course of the following description given with reference to the accompanying supporting drawing given by way of example and in which:

P16. 1 is a diagrammatic view in vertical section ofa grinding mill according to the invention; and

FIG. 2 diagrammatically shows an alternative means for supporting the rollers.

In the drawing, the numeral 1 designates a chamber of circular cross section of a grinding mill the base of which is equipped with a volute 2 forming a type of air distributor having tangential inlets because of deflectors 3. The lower portion of the chamber supports a fixed rolling track 4 of highstrength steel.

On the axis of the grinding mill, and at the bottom, there is disposed a vertical shaft 5 driven rotatively from a horizontal shaft 6 through the medium ofa reduction gear formed by a pair of bevel gears 7, 7 and incorporated in the apparatus of independent thereof. The vertical shaft 5 rests on an abutment 8 and is guided by bearings 9 and W.

The upper end of the shaft 5 is fast with a plate 10 disposed at the bottom of the grinding mill and wholly or partly covering the base thereof.

The rollers 11, which are adapted for being applied by centrifugal force against the rolling track 4 located at a level higher than that of the plate 10, are supported from plate 10.

In the constructional form shown in FIG. 1, each roller 11 is rotatable about a central spindle 12 which is articulated to the plate 10 through the mediumof a picot 13 having its axis perpendicular to the diametral plane defined by the shaft 5 and the spindle 12.

In the constructional form in FIG. 2, each roller 11 is rotatable about a spindle 12, one end of which is fast with a stirrup l4! movable rotatively with respect to the plate 10. For example, the stirrup can swing or rock about two coaxial pivots 15 and 15, it being understood that these articulations can be obtained by any other suitable elastic system.

The spindles 12 or 12 of the rollers lll may be designed in such manner as to receive supplementary counterweights 16 of variable weight which are intended to modify, at constant driving speed, the pressure exerted by the rollers 11 on the rolling track 43.

The crude product is introduced through a chute 17, which may be located laterally or axially, since the center of the grinding mill is unoccupied, Moreover, blades 18, or any other device designated to throw the crude product on to the rolling track 4 for the rollers, may be fast with the plate 10.

When the shaft 5 is driven rotatively, the rollers 11 are applied by the centrifugal force against the rolling track 4 located above said plate and, while the product to be ground is introduced through the chute 17, an air vortex coming from the volute 2 transverse the mill from bottom to top between the rollers ill and the rolling track 4, stirring up the product in the process of being ground, in conjunction with the blades 18, and entraining the ground grains through the outlet 19 into a selector or separator disposed at the top. The separator allows only those particles which have attained the required fineness to pass; the other particles drop back by gravity to the bottom of the mill. They are picked up by the blades 18 and subjected anew to the action of the rollers. It is to be noted that the separator (not shown) could be arranged in the inside of the chamber 1, since the central portion thereof is clear due to the arrangement according to the invention.

ln addition to the advantages already mentioned concerning the possibility of having an axial feed for the purpose of achieving a better distribution of the product over the wall of the grinding mill, the possibility of arranging the separator in the chamber, the absence of interference with the outlet circuit of the air which eliminates the risks of congestion of the apparatus, the simplification of lubrication and of the achievement of tightness due to the shortening of the shaft 5, with a better behavior under the dynamic stresses, it is possible to mention that the spindles 12, or 12' of the rollers are perfectly accessible and free from above, so that they can be placed in position and removed very easily.

Moreover, the possibility of adding the counterweights 16 to modify the pressure exerted by the rollers 11 on the rolling track 4 enables the grinding mill to be adapted to the nature of the product to be ground and to the fineness sought.

According to another variant of the invention one or more levels of supplementary rolling tracks such as are shown in dash lines at 4 may be placed above the rolling track 4 and on each of these supplementary tracks there acts a system of rollers supported from the same plate or from different plates. Systems of deflectors, such as that shown in dash lines at 20, can be provided to pick up the stream of air charged with the product which has undergone a first grinding at the level 4 and introduce it at the successive levels 4', or further where it undergoes secondary, tertiary, etc. grinding operations. These deflectors 20 may be designed in such manner as to effect a selection of the product between two successive levels. In this way, it is possible to effect, in a single operation, grinding to very high degrees of fineness, while considerably reducing the recycling circuits of the product and greatly increasing the output of the apparatus.

It is obvious that the constructional forms described have been given all by way of example and that many modifications may be made therein without thereby departing from the scope of the present invention as defined in the appended claims.

lclaim:

l. A grinding mill comprising a housing defining a grinding chamber having a vertical axis, a rotatable supporting plate in said chamber at the bottom thereof, a rolling track fixed in said housing at a level above said plate, rollers pivotably supported on said plate for traveling along said track as the plate rotates and being urged against said track by centrifugal force, means for introducing material to be ground into said chamber at the top thereof so that the material descends in the chamber and is introduced between the roller and track, means for producing an airflow in the chamber which conveys the ground material upwardly in an axial central region of the chamber, for external discharge at the top thereof, the latter said means comprising an air distributor encircling said chamber at the level of the plate, and means for rotating said plate including a shaft coupled to said plate and disposed in entirety thercbeneath for being driven in rotation from below said plate while leaving the entire region above the plate completely open.

2. A grinding mill as claimed in claim I, wherein said air distributor comprises a volute having tangential air inlets into said chamber.

3. A grinding mill as claimed in claim 1 comprising means rotatably supporting each roller and pivotably connected to said plate.

4. A grinding mill as claimed in claim 3, wherein the means supporting each roller comprises a stirrup rotatable with said plate and having two arms each pivotably supported on said plate, and a support shaft fixed to said stirrup between said arms, said rollers each being mounted on a support shaft of a respective stirrup.

5. A grinding mill as claimed in claim 1 comprising at least one further track fixed in said housing at a level above the first said track, and further rollers for each track. 

1. A grinding mill comprising a housing defining a grinding chamber having a vertical axis, a rotatable supporting plate in said chamber at the bottom thereof, a rolling track fixed in said housing at a level above said plate, rollers pivotably supported on said plate for traveling along said track as the plate rotates and being urged against said track by centrifugal force, means for introducing material to be ground into said chamber at the top thereof so that the material descends in the chamber and is introduced between the roller and track, means for producing an airflow in the chamber which conveys the ground material upwardly in an axial central region of the chamber, for external discharge at the top thereof, the latter said means comprising an air distributor encircling said chamber at the level of the plate, and means for rotating said plate including a shaft coupled to said plate and disposed in entirety therebeneath for being driven in rotation from below said plate while leaving the entire region above the plate completely open.
 2. A grinding mill as claimed in claim 1, wherein said air distributor comprises a volute having tangential air inlets into said chamber.
 3. A grinding mill as claimed in claim 1 comprising means rotatably supporting each roller and pivotably connected to said plate.
 4. A grinding mill as claimed in claim 3, wherein the means supporting each roller comprises a stirrup rotatable with said plate and having two arms each pivotably supported on said plate, and a support shaft fixed to said stirrup between said arms, said rollers each being mounted on a support shaft of a respective stirrup.
 5. A grinding mill as claimed in claim 1 comprising at least one further track fixed in said housing at a level above the first said track, and further rollers for each track. 